The mouth of the wicked is filled with curses, lies, and cheating. Nothing stops him. With curses
we must not think of the third commandment, but of the cursing of fellow men, to so hurt and humiliate them. His tongue causes trouble and brings about injustice. The mouth or tongue is a strong weapon. You can really slash an opponent with it. Think of the destructive force of propaganda such as was waged by Nazi-Germany in World War II. Destruction of people has humiliating words as its source. Presumably, Paul cites this Psalm in Romans 3:14; he indicates that all men are sinners, also God’s covenant people, Their mouth is full of curses and bitterness.
Then he refers to their deeds in Romans 3:15: Their feet are swift to shed blood
; and disdain for God is part of it, as in Romans 3:18: There is no fear of God before their eyes.
In villages, quiet places, or rural areas the wicked lays in ambush. That way, he has little chance of witnesses of his crime. In hidden places he kills the innocent. His eyes dart for defenseless people. It sounds like the army of the poor,
or one could say the pious people of God.
Three variants of his cunning actions: to ambush where it is quiet. Kill the innocent on the sly. The prep work is very important: watch carefully if there are weak people around. Think of the power of espionage. With terrorism happening, we also recognize this Psalm. Through all of this, the wicked increases his power as well as his possessions.
7 His mouth is filled with cursing and deceit and oppression; under his tongue are mischief and iniquity.